Programming from scratch [closed]

Answer 1

what you're talking about used to be called a 'monitor' program. you might get some interesting info at osdev.org and taking a look at colorforth.

[afterthought] google Rick Hohensee's ramblings on comp.lang.forth also.

[much later afterthought] to really get to basics, get a plug-in circuit breadboard, some old EPROMs, a 5VDC power supply and a 25VDC power supply (24 ought to work, it's more common). Use pullup or pulldown resistors on the address and data lines, and switches to supply ground or power to the address and data lines. Step through the addresses using the switches, and enter the data as ones and zeros on the data bus, programming each with a pulse from the 25V. I've never actually done this manually, but I once wrote a program (http://jc.unternet.net/hacks/?1994-01-01-01) to do this from a Centronics port, and burned several programs that way. This was back in the day when Intel would send you free books for all their processors and auxiliary chips, complete with detailed instruction sets and timing.

When done, connect your processor to the EPROM, give it some juice, and watch what happens. Maybe make it strobe some LEDs or something before you start trying to integrate keyboards and monitors.

Answer 2

You can acquire a microcontroller prototyping board such as Arduino, Beagleboard or MPLAB PIC board, and then create a machine monitor program that can load and execute your other programs in user space.

You can program those microcontrollers in C or their respective instruction sets.

Hook up an LCD display to that MCU board and you have a monitor. Hook up a keyboard and mouse to it and you have controls. (You can even write your own trap handlers for writing to LCD and reading inputs from keyboard and mouse to understand how interrupts and exceptions work at low level. If you want to go lower, you will have to look at MCU pin-outs for interrupt control lines and timing diagrams).

Voilà! You've designed your own computer from scratch!

To answer your question about C, compilers for the first programming languages were written in assembly, and compilers for assembly were written in machine code.

Answer 3

The problem you're describing is most commonly referred to as bootstrapping (and its' relationship to the chicken and egg problem). That specific link is for compilers, but you have the same problem in many areas - hardware, operating systems, etc., with similar solutions.

Answer 4

I can't tell you about hardware but if you want to build your own operating system, you can do that. It's a lot of work, but very rewarding. jcomeau_itcx already mentioned osdev.org. There's also the alt.os.development newsgroup, although it's been extremely quiet over the past couple of years - but check out the archive if you can find it.

Sounds like you're not put off by all the "Don't do it!" warnings... that's good :-) You can learn about boot sectors and write your own in a few days, and then you'll see something on the screen and know that you're on your way.

Many people recommend that you do not write your own boot sector, because it's not strictly part of the operating system. They recommend that you boot using GRUB or similar. I disagree, partly because I wanted to learn how the computer booted, but also partly because I found it easier to write my own boot sector than to figure out how to use GRUB!

C is the best language for writing an OS, because it's high-level enough for you to be productive but low-level enough for you to work directly on the processor. Many people use gcc, but you can also use Visual C++ or whatever (but compile in C, not C++, and you do need a compiler that supports inline assembler and can generate functions with no prolog/epilog.) You can write your code on your regular PC and then run it in a virtual machine - I prefer bochs because it's got a built-in debugger, but there are others.

Some tips for getting started on your OS (after you've sorted out your boot sector)... Intel IA32 is the most readily available processor (because it's in almost every PC) and most OS devers prefer it, so you can get more advice about it than about other platforms. I don't know whether they do this any more, but Intel sent me hard copies of their IA32 Software Developer's Manual - free of cost, but invaluable. You could work in real mode (16-bit, segments, no protection between apps... think Windows 3.1) but I reckon it's worth the effort to get into 32-bit protected mode (rather tricky) and be a bit more modern. Virtual memory (paging) is optional, but I did it because my original motivation for writing an OS was to learn just how 32-bit protected mode provided protection between apps.

It will be a long journey. I started my OS in 2004, working in the evenings, but then I started my business in 2006 and haven't had any time for it since. So it's a long way from being finished!

If you're curious, do it. You'll really enjoy it. And if you don't, you can stop.

Answer 5

You can't do what you seek terribly conveniently on most modern PC-style computers, but there are many inexpensive (sub-$100, or even sub-$50) kits available for programming smaller single-chip micros. A typical micro will have a few dozen pins which can be driven high and low under program control, along with a processor, some RAM (typically 256 bytes-8K or so), and some flash memory for code (typically 8K-128K or so). The development kits will typically have a processor with some pins attached to LEDs or an LCD display, and with other wires attached to a few buttons. The boards will also include circuitry so you can develop your software on a PC, connect a USB cable, and transfer your code into the chip.

Embedded programming is fun. Gives some of the feel of 'old-school' programming, with some newer modern conveniences.

Answer 6

I made the beginnings of an operating system with a computer I designed and cobbled together years ago (I think that would be about 1985 or so). It is decent fun and you learn a lot doing it. Good success on your project!

The answers people have been giving you about a platform you could use to develop your operating system have been of the hardware variety. You would have to spend a bit of $$. Assuming you have access to a computer you might consider using a virtual computer like QEMU, or Oracle's Vbox and develop an os for that. If you have a mac, I really like Q as the interface makes the virtual computer even look like one. I think other posts here have probably mentioned osdev.org. That is a great place to bounce ideas off other DIYers, and get some help getting started. Good success to you.

CHEERS